probe point "process(PATH).library("/lib64/libc.so.6").function("open") no match ERROR.

[maliubiao]

I am trying to trace functions in libc .
Do nm /lib64/libc.so.6 |grep open ,  actually there is a weak symbol open,
When I use malloc instead of open in function("open"),  It works ,  in
the handler  the result of probefunc() is __libc_malloc.
__libc_malloc is a T symbol, which is in the CODE segment.

Is there a way  to trace weak symbol  or  to find out  what symbol  do
a weak symbol actually refer to?